This invention is directed generally to circuit breakers, and more specifically, to the trip cross bar and the trip armature assembly components required to operate the tripping mechanism of a circuit breaker.
Circuit breakers are well-known and commonly used to provide automatic circuit interruption to a monitored circuit when undesired overcurrent conditions occur. Some of these overcurrent conditions include, but are not limited to, overload conditions, ground faults, and short-circuit conditions. The current interruption is usually achieved by having a movable contact, which is attached to a movable blade, that separates from a stationary contact, which is attached to a stationary arm or blade. A tripping mechanism is the component that drives the tripping action using, in general, a spring-biased latch mechanism to force the movable blade, and therefore the movable contact, away from the stationary contact.
A part of the tripping mechanism is the trip cross bar that is used as a means to activate a blade mechanism, which automatically moves the movable blade to an open position. The trip cross bar is generally mounted on a frame that is connected directly or indirectly to the circuit breaker housing. For example, in a prior art circuit breaker the trip cross bar must first be riveted to a latch and only then it is possible to attach the trip cross bar to a supporting fitting. Once attached to the supporting fitting the trip cross bar is rotatably supported by a supporting pin which is held in place by the supporting fitting and a side plate of a switch mechanism. A need exists for an improved circuit breaker design that requires fewer parts, is easier to assemble, and is compact in design. Given the position of the trip cross bar in the circuit breaker, the trip cross bar design may affect how other components of the circuit breaker are assembled and, also, how other components are shaped and dimensioned. In particular, space is needed inside the circuit breaker to assemble the various components of the circuit breaker, and the trip cross bar gets in the way.
It is, therefore, an object of this invention to provide easy assembly of a circuit breaker by providing a trip cross bar that is the last component to be assembled, using a top-down assembly method.
One type of tripping mechanism used in a circuit breaker is a thermal tripping unit. When the current reaches a predetermined value, which is generally based on a percentage of the rated current for a period of time, the tripping unit is activated. The tripping unit passes the current through and thereby heats a bimetal, hence, causing the bimetal to bend. As a result, the bimetal, now bent, contacts and activates the trip cross bar. The current also passes through a magnetic trip armature which causes it to rotate into engagement with a magnetized pole, activating the trip cross bar. The trip cross bar, when activated, causes a latch mechanism to rotate on movable blade away from the stationary contact. The end result is that the circuit breaker is in a tripped position, opening the circuit. However, an improved manner of connecting the magnetic trip armature to the armature supporting frame permits the development of a smaller, more efficient, and more economical circuit breaker.
It is, therefore, another object of this invention to provide a magnetic trip armature that can be easily and simply connected to an armature return spring and to an armature supporting frame. This is accomplished by having the magnetic trip armature snap into the armature supporting frame and by being held secure in all orientations by the armature return spring, using a top down assembly wherein late point assembly allows other parts to be placed in the circuit breaker without interference.
Briefly, in accordance with the foregoing, a circuit breaker for interrupting the flow of current upon the detection of excess current or temperature is provided which comprises a housing, a trip armature plate, a trip armature frame, and a bias spring. The trip armature plate has at least two pivot tabs extending laterally on opposite edges that are inserted into a pivot elongated slot, which is located at an open end of the trip armature frame, and a pivot aperture, which is located at the opposite end of the trip armature frame, respectively. A bias spring is used for securing the pivot tabs into the pivot elongated slot and the pivot aperture, and for urging the trip armature plate pivotably outwardly about the pivot tabs away from the trip armature frame.
Additionally, a trip cross bar is provided in the circuit breaker. The trip cross bar can have, optionally, two fingers that are used to engage optional circuit breaker accessories and that are located asymmetrically to allow the interchangeability of the accessories. During top down assembly, the trip cross bar is the last component that is assembled into the circuit breaker in order to allow the easy installation of other components, including the trip armature frame and trip armature plate. The connecting location of the trip cross bar is in a central position for allowing actuation of the trip cross bar by a central, left, or right bimetal.